1. Field of the Invention
The present invention generally relates to transflective liquid crystal displays (LCD), and particularly to pixel structures for transflective LCD.
2. Description of the Related Art
A transflective LCD conventionally operates to display images under light illumination coming from an external light source and a backlight embedded in the display system. The transflective display mode is advantageous because it has lower power consumption compared to transmissive displays.
FIG. 1 is a general schematic view of a pixel structure known in conventional transflective LCD panels. The conventional transflective LCD panel includes the assembly of rear and front substrates 100, 160, respectively made of transparent materials. Display is viewed from the side of the front substrate 160 while the backlight (not shown) is placed on the side of the rear substrate 100. A liquid crystal layer 150 is sandwiched between the rear substrate 100 and the front substrate 160 to modulate incoming light and thereby achieve image display.
The pixel electrode structure conventionally includes a reflective electrode 126 placed adjacent to a transmissive electrode 124. Both reflective electrode 126 and transmissive electrode 124 thereby respectively define a reflective area and a transmissive area. The reflective electrode 126 is composed of a reflective plate made of a metallic material having suitable reflectance, while the transmissive electrode 124 is conventionally made of a transparent conductive material such as indium-tin-oxide or indium-zinc-oxide.
In the transmissive area, light 182 coming from a backlight (not shown) travels through the transmissive electrode 124, and transmits via the liquid crystal layer 150 to emerge at the viewer side for displaying images. In the reflective area, light 184 comes from an external light source on the viewer side (not shown), travels through the liquid crystal 150, reflects on the reflective electrode 126, and travels again through the liquid crystal 150 to emerge at the viewer side.
One factor indicative of the LCD performance is its optical efficiency. The optical response depends upon the cell retardation of the liquid crystal, characterized by the product “dΔn”, wherein d is the cell gap and Δn is the average birefringence of the liquid crystal within the cell gap. In the transmissive area, the optical retardation conventionally is optimal for dΔn˜(½)λ, while in the reflective area it is optimal for dΔn˜(¼)λ. One technical issue encountered in a conventional transflective LCD such as the one described in FIG. 1 is that the same cell retardation occurs in both reflective area and the transmissive area. No optimal optical performance therefore can be obtained in both reflective and transmissive areas of the conventional transflective LCD.
Therefore, there is presently a need for a transflective liquid crystal display that has improved optical characteristics in both reflective and transmissive areas.